No abstract

Fiber Bragg grating (FBG) is fabricated in the microfiber by the use of femtosecond laser pulse irradiation. Such a grating can be directly exposed to the surrounding medium without etching or thinning treatment of the fiber, thus possessing high refractive index (RI) sensitivity while maintaining superior reliability. The grating in the microfiber may have a number of propagation modes in its transmission spectrum, depending on the fiber diameter, and the higher order of mode has larger RI sensitivity. The RI sensitivity also depends on the fiber diameter and a smaller diameter corresponds to a large sensitivity. The maximum sensitivity obtained is ϳ231.4 nm per refractive index unit at the refractive index value of ϳ1.44 when the fiber diameter is ϳ2 m. The FBG fabricated in the microfiber has high potential in various types of optical fiber There has been increased research interest in optical microfibers/nanofibers in recent years [1-4] because of their many unique and interesting properties. An optical microfiber/nanofiber essentially consists of only fiber core, surrounded by air. When light travels along the fiber, it is tightly confined to the fiber core owing to the large refractive index (RI) contrast between the core and air, while a large fraction of the guided light can propagate outside the fiber as the evanescent wave, which makes it highly sensitive to the ambient medium. The small size of the microfiber/nanofiber also provides excellent flexibility and convenient configurability, allowing the easy manipulation of the microfiber-/nanofiber-based devices with a complex topology. Many microfiber-/nanofiber-based fiber devices have been developed, with important applications in the area such as RI sensing [5][6][7][8][9][10].Fiber Bragg grating (FBG) is one of the basic optical fiber components that have wide applications. However, FBG is intrinsically insensitive to the external RI change, as it is not directly exposed to the surrounding medium. Although such a difficulty can be alleviated by thinning or etching of the fiber after the FBG creation [11][12][13], the mechanical strength and durability of the sensing device are greatly reduced, which limits the applications of FBG-based RI sensors. In contrast, long period fiber grating (LPFG) is widely used as the RI sensor, owing to its intrinsically high sensitivity to the surrounding medium change in a large range [14]. However, the transmission dips of the LPFG are broad (typical of tens of nanometers) [12], resulting in a poor measurement accuracy. Meanwhile, the length of the LPFG is relatively large (typical of ϳ30 mm) [15], which limits its applications in accurate sensor devices.The FBG in microfiber can overcome the abovementioned difficulties because of its narrow bandwidth, small grating size, and good measurement accuracy. Moreover, the FBG can support the multiplexed system, showing significant advantages over the LPFG.A powerful tool for the FBG fabrication is a femtosecond laser, which allows the inscription of the FBG in almost any t...

Ultralong single-crystalline CoP nanowires were grown on porous Co foam via a vapor–solid reaction method and used for overall electrochemical water splitting in alkaline solution.

The structural and photophysical properties of tetradentate Pt(ppzOppz), Pt(ppzOpopy), Pt(ppzOczpy), and Pt(czpyOczpy) have been experimentally and theoretically explored. Single-crystal diffraction measurements provided accurate structural information. Electrochemical and photophysical characterizations revealed internal electronic energy levels in ground and excited states. (Time-dependent) Density functional theory calculation revealed electron distributions in transition processes of S → S and S → T → S. Electronic transition study indicated that Pt(ppzOppz) demonstrated mixed MLCT/LC states and Pt(czpyOczpy) showed MLCT-dominated states in S and T. Both Pt(ppzOpopy) and Pt(ppzOczpy) presented strong delocalized spin transition (DST) during intersystem crossing. Upon frame modification of Pt(ppzOczpy), we found that their S and T can be independently manipulated. These blue emitters showed a tunable and narrow emission band (the narrowest fwhm was 19 nm) with luminescence efficiency as high as 86%. The findings of the DST transition mode in the neutral Pt(II) complexes provide guidance for rational design of novel phosphorescent materials.

A series of Pt(ii) complexes with narrow emission spectra were systematically investigated and Pt(ppzOczpy-4m), rationally designed with predominantly 3LC(3ππ*) character in T1, was fabricated into efficient blue OLEDs via a solution process.

An amphiphilic metallic chelate−aromatic sulfonic iron was synthesized for the first time, characterized by Fourier transform infrared (FT-IR) spectroscopy, and then used in catalytic aquathermolysis of heavy oil both in the laboratory and field. The laboratory results showed that this new catalyst was efficient, universal, and superior to other efficient catalysts we have synthesized before; in addition, for EX35 heavy oil, it led to a evident viscosity reduction by 90.66% at 200 °C with 14.66% in conversion of heavy contents to light contents. To evaluate the its performance, the structure and group composition of heavy oil was analyzed by FT-IR, thin-layer chromatography−flame ionization detection (TLC-FID), gas chromatography/mass spectrometry (GC/MS), 1H NMR, and elemental analysis (EL) before and after the aquathermolysis. It is found that the changes of the composition and structure of the heavy oil can lead to the viscosity reduction. In field tests of G61012 and G6606 wells in the Henan oilfield, the production increased by 188.7 and 217 t in 14 d (an observed period) after catalytic aquathermolysis technology, respectively, and the viscosity of oil reduced at a rate of 79.66% and 82.25%.

A simple linear cavity erbium-doped fiber laser based on a Fabry-Perot filter which consists of a pair of fiber Bragg gratings is proposed for tunable and switchable single-longitudinal-mode dualwavelength operation. The single-longitudinal-mode is obtained by the saturable absorption of an unpumed erbium-doped fiber together with a narrow-band fiber Bragg grating. Under the high pump power (>166mW) condition, the stable dual-wavelength oscillation with uniform amplitude can be realized by carefully adjusting the polarization controller in the cavity. Wavelength selection and switching are achieved by tuning the narrow-band fiber Bragg grating in the system. The spacing of the dualwavelength can be selected at 0.20nm (~ 25.62GHz), 0.22nm (~ 28.19GHz) and 0.54nm (~ 69.19GHz). ©2009 Optical Society of AmericaOCIS codes: (000.0000) General; (000.2700) General science. References and links1. N. J. C. Libatique, and R. K. Jain, "Precisely and rapidly wavelength-switchable narrow-linewidth 1.5µm laser source for wavelength division multiplexing applications," IEEE Photon. Technol. Lett. 11(12), 1584-1586 (1999). 2. Z. Chen, S. Ma, and N. K. Dutta, "Stable dual wavelength mode-locked Erbium-doped fiber ring laser," in Frontiers in Optics, OSA Technical Digest, paper

No abstract